3 Answers
3

In this example, やっぱり functions as something like "as I thought" and shows that the speaker had a preexisting suspicion that a certain matter was indeed true. なるほど shows that a greater understanding of the surrounding context has been gained from the confirmation of the fact referred to by そう. So yes, it does make sense.

EDIT (for the updated question)

I can't think of any examples where なるほど could be swapped with やっぱり, or vice versa. In my mind, なるほど and やっぱり are in different categories. I have to partially disagree with one of Amanda's comments by pointing out that なるほど doesn't have the same "I should have guessed" meaning as やっぱり. It can, however, mean "That makes sense." なるほど merely shows that your mental picture of something (for instance, a course of events, the inner workings of a machine, or the reasoning leading to a certain conclusion) has been filled in by what you were just told. You wouldn't use なるほど when someone is stating a simple fact ("I like ice cream," "I'm not good at playing the piano," etc), but you would when that fact is part of a surrounding context through which the speaker intends to draw you to a greater understanding of the current topic of conversation.

So, can we say なるほど is as neutral as "I see" in English, unlike the biased やっぱり?
– LukmanJun 3 '11 at 4:46

It's not quite as neutral as そうですか, but much more neutral than やっぱり.
– Amanda SJun 3 '11 at 5:04

You mean there is a little bit of suspicion in なるほど? And, in term of neutrality: そうですか > なるほど > やっぱり? >____<
– LukmanJun 3 '11 at 5:08

Another thing, what do I use if what actually happens is the opposite of my previous suspicion?
– LukmanJun 3 '11 at 5:11

Yeah, なるほど is a little bit like "oh, I should have guessed!" or "oh, that makes so much sense!" I wouldn't say it to someone's face if they told me something negative about themselves, but I might if I was hearing the news secondhand.
– Amanda SJun 3 '11 at 5:12

Interesting discussion. It has been a while since I lived in the land of the rising sun (1973-79). My language skills (although greatly deteriorated with age:-)) were gleaned from the surfing and farming types from Miura Hanto. I always used naruhdo in the context of "interesting" or "oh, I see". For example, if I had no bottle opener and someone shows me a new way to open it..I would say "Naruhodo jyan". This could be used every time you were introduced to something new; a bit of gossip; a new/different way of doing something. Yappari on the other hand was a term used to verify something???For example ...I tell you your girlfriend is messing around. We walk around the corner and there she is kissing another guy. He would say "Yappari da". As to say you were right, or wrong. Yappari can also be used to change ones mind. For example. Lets go drink beer, your wife won't mind...Ok...After some thought about the wife.."Yappari, I should not go drink beer, I shall go home. Both naruhodo and yappari can be used as "I see". Naruhodo as a direct I see I learned something and Yappari as I see in the good or bad decision making process (I see my wife being pissed that I am out drinking beer, therefore I am going home).